1. Field of Invention
This invention is related to embedding watermarks in input images to form watermarked output images.
2. Description of Related Art
With the advent of digitization of images, digital image distribution and digital video availability, the “hiding” of information in digital images for purposes such as copyright protection has become a substantial issue for image publishers and authors. The process of imbedding information in a digital image is known as “watermarking”. Such watermarks must be secure, robust to intentional corruption and to compression processing, not unreasonably complex to embed and extract, and compatible and interoperable with conventional image processing systems. The watermark is generally invisible to a viewer. However, in some applications, it is desirable to produce a visible watermark that can be removed by an authorized image decoder and that can not be removed by an unauthorized decoder.
Many watermark algorithms have been proposed. However, only a few watermark algorithms have been designed for printed images. U.S. Pat. No. 5,734,752 to Knox discloses a method of using stochastic screens to create correlation-based digital watermarks. The concept of conjugate halftone screens for watermarking is proposed in U.S. Pat. No. 5,790,703 to Wang. The methods disclosed in Knox and Wang might not be suitable for applications which require dynamically changing watermark information, because the watermarks in those methods can only be embedded during the screen design process for the halftone screen that will be used when printing a given image. U.S. Pat. No. 5,946,103 to Curry discloses a method that uses glyphs to digitally watermark a printed document. However, glyph encoding typically generates images with noticeable structures. This makes this method suitable only for specific applications.